Field of the Invention
The present invention relates to a honeycomb structure. More particularly, it relates to a honeycomb structure which is excellent in pressure resisting strength of circumferential portion and in thermal shock resistance.
Description of Related Art
Ceramic honeycomb structures excellent in thermal resistance and corrosion resistance have been employed as carriers for catalyst devices or filters for use as environmental measures, collection of specific material or the like in various fields of chemistry, electric power, steel industry, and the like. In the honeycomb structures, a structure resembling a honeycomb built by bees (honeycomb structure) is formed by partition walls to define cells that become through channels for a fluid. Such honeycomb structures are used as catalyst carriers onto which catalyst for purification of exhaust gas is loaded in exhaust gas purification devices to purify the exhaust gas discharged from internal combustion engines such as car engines. Furthermore, in the honeycomb structures, open ends of the cells in both end faces are alternately plugged to obtain plugged honeycomb structures, and the honeycomb structures are also often used as diesel particulate filters to trap particulate matter discharged from diesel engines or the like.
When the exhaust gas is purified by a honeycomb structure, the honeycomb structure is sometimes used, for example, in an exhaust gas purification device in which the honeycomb structure is contained in a can member having an inflow port through which the exhaust gas flows inside and an outflow port through which the purified exhaust gas flows outside. Hereinafter, the containing of the honeycomb structure into a can member of the exhaust gas purification device as described above may be referred to as “canning”.
Heretofore, when such a honeycomb structure is contained in the can member of the exhaust gas purification device, damages are sometimes generated in a circumferential portion of the honeycomb structure. Therefore, there have been suggested various technologies to improve the pressure resisting strength of the circumferential portion of the honeycomb structure (e.g., see Patent Documents 1 to 4).
In Patent Document 1, for a honeycomb structure in which cross sections of cells are hexagonal, there has been described a technology in which a thickness of partition walls of a circumferential portion is set to be larger than a thickness of partition walls of a central portion. Furthermore, in Patent Document 2 and Patent Document 3, for a honeycomb structure in which cross sections of cells are quadrangular, there has been described a technology in which a thickness of partition walls of a circumferential portion is set to be larger than a thickness of partition walls of a central portion. Furthermore, in Patent Document 4, there has been described a technology in which a hydraulic diameter of cells positioned at the edge of at least one of four sides constituting a rectangular or square cross section of a honeycomb structure is made to be smaller than a hydraulic diameter of other cells.
[Patent Document 1] JP-A-H11-270334
[Patent Document 2] JP-A-H11-277653
[Patent Document 3] WO 02/011884
[Patent Document 4] JP-A-2000-238153